*MRC Protein Phosphorylation and Ubiquitylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, U.K.
†Centre d'Immunologie de Marseille-Luminy, Parc Scientifique & Technologique de Luminy, Case 906, 13288 Marseille cedex 09, France.
Biochem J. 2014 Aug 1;461(3):531-7. doi: 10.1042/BJ20140444.
IKKβ {IκB [inhibitor of NF-κB (nuclear factor κB)] kinase β} is required to activate the transcription factor NF-κB, but how IKKβ itself is activated in vivo is still unclear. It was found to require phosphorylation by one or more 'upstream' protein kinases in some reports, but by autophosphorylation in others. In the present study, we resolve this contro-versy by demonstrating that the activation of IKKβ induced by IL-1 (interleukin-1) or TNF (tumour necrosis factor) in embryonic fibroblasts, or by ligands that activate Toll-like receptors in macrophages, requires two distinct phosphorylation events: first, the TAK1 [TGFβ (transforming growth factor β)-activated kinase-1]-catalysed phosphorylation of Ser¹⁷⁷ and, secondly, the IKKβ-catalysed autophosphorylation of Ser¹⁸¹. The phosphorylation of Ser¹⁷⁷ by TAK1 is a priming event required for the subsequent autophosphorylation of Ser¹⁸¹, which enables IKKβ to phosphorylate exogenous substrates. We also provide genetic evidence which indicates that the IL-1-stimulated, LUBAC (linear ubiquitin chain assembly complex)-catalysed formation of linear ubiquitin chains and their interaction with the NEMO (NF-κB essential modulator) component of the canonical IKK complex permits the TAK1-catalysed priming phosphorylation of IKKβ at Ser¹⁷⁷ and IKKα at Ser¹⁷⁶. These findings may be of general significance for the activation of other protein kinases.
IKKβ{NF-κB（核因子κB）抑制剂激酶β}是激活转录因子 NF-κB 所必需的，但 IKKβ 本身在体内如何被激活尚不清楚。一些报道发现它需要一种或多种“上游”蛋白激酶的磷酸化，但另一些报道则发现它需要自身磷酸化。在本研究中，我们通过证明在胚胎成纤维细胞中由 IL-1（白细胞介素-1）或 TNF（肿瘤坏死因子）或在巨噬细胞中由激活 Toll 样受体的配体诱导的 IKKβ 的激活需要两个不同的磷酸化事件来解决这一争议：首先，TAK1[TGFβ（转化生长因子β）激活激酶-1]催化 Ser¹⁷⁷的磷酸化，其次，IKKβ催化 Ser¹⁸¹的自身磷酸化。TAK1 催化的 Ser¹⁷⁷磷酸化是随后 Ser¹⁸¹自身磷酸化的引发事件，这使 IKKβ能够磷酸化外源性底物。我们还提供了遗传证据，表明 IL-1 刺激的、LUBAC（线性泛素链组装复合物）催化的线性泛素链的形成及其与经典 IKK 复合物的 NEMO（NF-κB 必需调节剂）成分的相互作用允许 TAK1 催化 IKKβ 在 Ser¹⁷⁷和 IKKα 在 Ser¹⁷⁶的引发磷酸化。这些发现可能对其他蛋白激酶的激活具有普遍意义。
